Abstract: In order to improve the performance of materials in high-field magnets, understand the behavior of materials in complex environments, and study the phase stability prediction of Nb3Sn superconducting fiber materials under strong magnetic fields, Nb3Sn superconducting fiber materials were obtained by ball milling mixed with niobium powder, tin powder, and iron powder after multi-process processing such as pressing, sintering, and polishing. After the material was treated in a high magnetic field heat treatment device, the phase stability of the material was predicted by experiments under different treatment methods, different magnetic field intensity, annealing temperature and milling time. The results show that the phase stability of the material can be significantly improved by using high magnetic field heat treatment. The milling time is set to 2.8h, the grain size of the raw material is moderate, and the magnetic parameters are high. At 7.5T magnetic field intensity, the NB-rich phase of the material has obvious orientation, and the grain smoothness increases. At the annealing temperature of 650℃, the NB-rich phase is obvious, and the distribution uniformity is strong, and a large number of NB-rich phases appear in the layered morphology between the grains, and the phase stability of the material is high.